1. Field of the Invention
The present invention relates, in general, to a high strength and low shrinkage polyester yarn and method of preparing the same and in particular, to a high strength and low shrinkage polyester yarn, which has desirable resistance to external load and excellent dimensional stability, and is useful as an industrial yarn with uniform shrinkage and excellent dimensional stability during a post-process for application to tarpaulins and truck covers, and a process for its preparation.
2. Description of the Prior Art
Having excellent physical and chemical properties, industrial uses for polyester yarn continuously increase. Particularly, high strength polyester yarn is used as a base textile of coated textiles such as tarpaulins and truck covers. However, because tarpaulins and truck covers are prepared by coating the base textile with PVC at 180 to 230xc2x0 C., the high strength polyester yarn is nonuniformly shrunk due to its poor shrinkage property during a coating process, thus lacking dimensional stability. Furthermore, the high strength polyester yarn shrinks considerably during a post-process to degrade the quality of the coated textile. Accordingly, there remains a need to develop a high strength and low shrinkage polyester yarn.
One of processes of preparing a low shrinkage polyester yarn is a warp drawing process in which undrawn yarn (UDY) or partially oriented yarn (POY) wound after a spinning process is drawn, heat-treated, and relaxed using separate devices. For example, Korean Patent Publication No. 1995-0000717 discloses the warp drawing process, in which undrawn yarn or partially oriented yarn is drawn and heat-treated to prepare a polyester yarn with tenacity of 8.0 g/d or higher, dry-heat shrinking percentage (190xc2x0 C.) less than 2%, and elongation at break of 15 to 25%. However, the warp drawing process has disadvantages of high equipment cost, reduced productivity, and increased production costs because of the separate drawing device.
An alternative process for preparing the low shrinkage polyester yarn is a direct spinning drawing process disclosed in Japanese Patent Laid-open Publication No. Sho. 46-6459, in which spinning, drawing, and relaxing steps are continuously performed. Korean Patent No. 0193940 proposes a method of preparing a high elongation and low shrinkage polyester yarn having a total draw ratio of 5.0 to 6.5, relaxation ratio of 10 to 15%, and fineness of 7 to 15 deniers by the direct spinning drawing process. However, the direct spinning drawing process is disadvantageous in that dry-heat shrinkage percentage is a high 3.3% when relaxation ratio is 12.7% even though residence time of the polyester yarn on a roller is increased by slowing a spinning speed to 600 m/min.
As described above, in the case of preparing the low shrinkage polyester yarn by the direct spinning drawing process, if the total draw ratio is increased to obtain a high strength yarn, a degree of orientation in the yarn is increased, thus undesirably increasing its shrinkage ratio.
Additionally, if relaxation percentage is increased so as to reduce shrinkage, trembling of threads on a godet roller is undesirably increased to cause yarn breakage, thereby reducing workability.
Meanwhile, U.S. Pat. No. 5,277,858 suggests a method of preparing a low shrinkage polyester yarn having tenacity of 7.2 g/d or higher, shrinkage percentage less than 2.0% at 177xc2x0 C., and shrinkage percentage less than 4.5% at 200xc2x0 C. by the spinning-drawing continuous process. But this method is disadvantageous in that a separate heating device is needed, which is used in a heating roller box. Furthermore, Korean Patent Laid-open Publication No. 1998-028329 discloses a method of preparing a low shrinkage yarn, in which a heating and a cooling device, and a steam supplying device are additionally set between godet rollers. However, a large space as well as additional devices such as the heating and cooling device and the steam supplying device are needed so as to commercialize this method, thus reducing economic efficiency.
Therefore, the present invention has been made keeping in mind the above disadvantages occurring in the prior art, and an object of the present invention is to provide a high strength and low shrinkage polyester yarn, which has desirable resistance to external load and is useful as an industrial yarn with uniform shrinkage and excellent dimensional stability during a post-process for application to tarpaulins and truck covers.
It is another object of the present invention to provide a method of preparing the high strength and low shrinkage polyester yarn.